National Weather Service: Sulphur Mountain Radar Performance (Letter
Report, 10/16/98, GAO/AIMD-99-7).
Pursuant to a legislative requirement, GAO reviewed the Rose Institute
of Claremont McKenna College's study on the National Weather Service's
(NWS) Next Generation Weather Radar (NEXRAD) located on Sulphur
Mountain, California, focusing on whether the Sulphur Mountain NEXRAD:
(1) can provide timely and accurate information for warning of flash
floods; and (2) is intended to provide low-level data necessary to
predict wind shear for Los Angeles International Airport.
GAO noted that: (1) since the Sulphur Mountain NEXRAD was commissioned
in December 1994, the accuracy and timeliness of flash flood warnings
has improved for Ventura and Los Angeles counties; (2) from January 1992
through December 1994, 18 flash floods events were reported in Ventura
and Los Angeles counties; (3) however, from January 1995 through
February 1998, advanced warnings were issued for 17 of the 22 reported
events; (3) although the Sulphur Mountain radar is not the only source
of data on which flash flood warnings are issued, NWS officials believe
that the Sulphur Mountain NEXRAD is the primary reason for the increase
in advanced warning lead time because it provides advanced warning of
heavy precipitation, often before severe weather hits the California
coast; (4) users of the Sulphur Mountain NEXRAD data told GAO that the
information it provides is valuable, accurate, and timely; (5) despite
the improvements in flash flood warning lead time and user satisfaction,
NWS data show that the Sulphur Mountain NEXRAD is not consistently
meeting its 96 percent availability requirement; (6) from October 1995
through March 1998, the Sulphur Mountain NEXRAD was available as
required for 20 months; for the other 10 months, availability ranged
between 79 to 95 percent; (7) if the NEXRAD is not available as
required, it increases the risk that NWS will not have the data it needs
to accurately and quickly predict flash floods and other severe weather;
(8) NWS headquarters officials acknowledged the availability shortfalls
and stated that they are monitoring the failure rates of parts and are
attempting to reduce the failure rates or to more quickly replace the
parts that fail most often; (9) predicting wind shear at Los Angeles
International Airport is not part of NEXRAD's mission; (10) the Federal
Aviation Administration (FAA) uses three different systems to predict
wind shear at airports--Terminal Doppler Weather Radar (TDWR), Weather
Systems Processor (WSP), and Low Level Wind Shear Alert System (LLWAS);
(11) TDWR is being deployed at high traffic airports that experience
severe weather; (12) WSP is an enhancement to an existing air traffic
control surveillance radar that is to provide FAA with 80 to 95 percent
of the capability of TDWR; (13) WSP is to be installed at high to
moderate traffic airports that experience limited severe weather; (14)
LLWAS is used to supplement TDWR at nine high traffic airports at
greatest risk of severe weather and it is used at other airports that
will not get TDWR or WSP; and (15) Los Angeles International Airport
currently has LLWAS and is scheduled to get WSP in 2001.
--------------------------- Indexing Terms -----------------------------
REPORTNUM: AIMD-99-7
TITLE: National Weather Service: Sulphur Mountain Radar Performance
DATE: 10/16/98
SUBJECT: Weather forecasting
Radar equipment
Interagency relations
Storms
Transportation safety
Warning systems
Air traffic control systems
IDENTIFIER: NWS Next Generation Weather Radar
Ventura (CA)
FAA Automated Terminal Doppler Radar Warning System
FAA Low Level Wind Shear Alert System
Los Angeles (CA)
Los Angeles International Airport (CA)
FAA Weather Systems Processor
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Cover
================================================================ COVER
Report to Congressional Requesters
October 1998
NATIONAL WEATHER SERVICE - SULPHUR
MOUNTAIN RADAR PERFORMANCE
GAO/AIMD-99-7
Sulphur Mountain Radar
(511445)
Abbreviations
=============================================================== ABBREV
AIMD - Accounting and Information Management Division
ASOS - Automated Surface Observing System
ASR - Airport Surveillance Radar
AWIPS - Advanced Weather Interactive Processing System
EMRS - Engineering Management Reporting System
FAA - Federal Aviation Administration
GOES-Next - Next Generation Geostationary Operational Environmental
Satellite
LLWAS - Low Level Wind Shear Alert System
NEXRAD - Next Generation Weather Radar
NOAA - National Oceanic and Atmospheric Administration
NWS - National Weather Service
PUP - principal user processor
RDA - radar data acquisition
RPG - radar product generator
TDWR - Terminal Doppler Weather Radar
WFO - Weather Forecast Office
WSP - Weather Systems Processor
Letter
=============================================================== LETTER
B-279985
October 16, 1998
The Honorable Judd Gregg
Chairman
The Honorable Ernest F. Hollings
Ranking Minority Member
Subcommittee on Commerce, Justice,
State, and the Judiciary
Committee on Appropriations
United States Senate
The Honorable Barbara Boxer
United States Senate
In December 1994, the National Weather Service (NWS) began operating
a Next Generation Weather Radar (NEXRAD) located on Sulphur Mountain
in Ventura County, California. The radar was recently the focus of a
study by the Rose Institute of Claremont McKenna College. The
Institute concluded, among other things, that the location of the
radar prevented it from performing its mission to provide accurate
and timely information for warning of flash flooding in nearby
communities and wind shear at nearby airports.
Given the issues raised by the Rose Institute, Senate report 105-48
requested that we review the findings in the Rose Institute report.
As agreed with your offices, our objectives were to determine whether
the Sulphur Mountain NEXRAD (1) can provide timely and accurate
information for warning of flash floods\1 and (2) is intended to
provide low-level data necessary to predict wind shear for Los
Angeles International Airport.
--------------------
\1 NWS' Operations Manual defines a flash flood as a flood which is
caused by heavy or excessive rainfall in a short period of time,
generally less than 6 hours.
RESULTS IN BRIEF
------------------------------------------------------------ Letter :1
Since the Sulphur Mountain NEXRAD was commissioned in December 1994,
the accuracy and timeliness of flash flood warnings has improved for
Ventura and Los Angeles counties. From January 1992 through December
1994, 18 flash flood events were reported in Ventura and Los Angeles
counties. There was no advanced warning for any of the 18 events.
However, from January 1995 through February 1998, advanced warnings
were issued for 17 of the 22 reported events; the average warning
lead time for these was just over 2 hours. Although the Sulphur
Mountain radar is not the only source of data on which flash flood
warnings are issued, NWS officials believe that the Sulphur Mountain
NEXRAD is the primary reason for the increase in advanced warning
lead time because it provides advanced warning of heavy
precipitation, often before severe weather hits the California coast.
In addition, users of the Sulphur Mountain NEXRAD data told us that
the information it provides is valuable, accurate, and timely. For
example, officials from the Los Angeles County Department of Public
Works, who are responsible for constructing, operating, and
maintaining the flood control and water conservation facilities in
Los Angeles County, told us that the Sulphur Mountain NEXRAD has
significantly improved the quality and quantity of radar information
they receive and that it is substantially more detailed, accurate,
and timely than previous radars. In addition, the Director of
Emergency Services for Ventura County considers the radar "to be an
effective tool for identifying the appropriate level of response for
county emergency services during inclement weather."
Despite the improvements in flash flood warning lead time and user
satisfaction, NWS data show that the Sulphur Mountain NEXRAD is not
consistently meeting its 96 percent availability\2 requirement.
During the 30 months from October 1995 through March 1998, the
Sulphur Mountain NEXRAD was available as required for 20 months; for
the other 10 months, availability ranged between 79 percent to 95
percent. If the NEXRAD is not available as required, it increases
the risk that NWS will not have the data it needs to accurately and
quickly predict flash floods and other severe weather. NWS
headquarters officials acknowledged the availability shortfalls and
stated that they are monitoring the failure rates of parts and are
attempting to reduce the failure rates or to more quickly replace the
parts that fail most often. For instance, they told us that they are
installing fans to keep the transmitter, a component that has been
unreliable since the inception of the NEXRAD program, from
overheating. In addition, NWS officials told us that they are
working with different shipping companies to hasten the delivery of
replacement parts.
Predicting wind shear at Los Angeles International Airport is not
part of NEXRAD's mission. The Federal Aviation Administration (FAA)
uses three different systems, either alone or in tandem, to predict
wind shear at airports--Terminal Doppler Weather Radar (TDWR),
Weather Systems Processor (WSP), and Low Level Wind Shear Alert
System (LLWAS). TDWR is the "state of the art" wind shear detection
system that is currently being deployed at high traffic airports that
experience severe weather. WSP is an enhancement to an existing air
traffic control surveillance radar that is to provide FAA with 80 to
95 percent of the capability of TDWR. WSP is to be installed at high
to moderate traffic airports that experience limited severe weather.
LLWAS is a network of anemometers\3 that were originally installed in
the 1970s. LLWAS is used to supplement TDWR at nine high traffic
airports at greatest risk of severe weather and it is used at other
airports that will not get TDWR or WSP--typically lower traffic
airports. Los Angeles International Airport currently has LLWAS and
since it is an airport designated as having high to moderate traffic
and typically experiences limited severe weather, it is scheduled to
get WSP in 2001.
--------------------
\2 System availability is defined as the time that a system is
operating satisfactorily, expressed as a percentage of the time the
system is required to be operational.
\3 An anemometer is an instrument for measuring and indicating the
force or speed of wind.
BACKGROUND
------------------------------------------------------------ Letter :2
NWS began a nationwide modernization program in the 1980s to upgrade
observing systems, such as satellites and radars, and design and
develop advanced forecaster computer workstations. The goals of the
modernization are to achieve more uniform weather services across the
nation, improve forecasts, provide better detection and prediction of
severe weather and flooding, permit more cost-effective operations
through staff and office reductions, and achieve higher productivity.
Four major programs are included in this modernization: NEXRAD, the
Automated Surface Observing System (ASOS), the Next Generation
Geostationary Operational Environmental Satellite (GOES-Next), and
the Advanced Weather Interactive Processing System (AWIPS). NEXRAD,
ASOS, and GOES-Next--commonly referred to as the observing
systems--are operational, while AWIPS is scheduled to be deployed
nationwide in June 1999.
Ongoing problems--both developmental and operational--have surrounded
the modernization. For example, we have reported that the NEXRADs
have not always been operating when severe weather threatened, and
ASOS has fallen short of performance and user expectations.\4 We have
made specific recommendations and testified numerous times over the
past several years on these performance problems, developmental
problems, and problems relating to cost and schedule.\5 As a result
of its continuing problems, the NWS modernization has been
included--both in 1995 and 1997--on our list of high-risk government
programs.\6 Although NWS acknowledges that key problems confront the
new systems, it has found that the new radars and satellites have
improved forecasts and warnings.
As part of its modernization program, NWS plans to reorganize its
field office structure from 256 offices (52 Weather Service Forecast
Offices and 204 Weather Service Offices), to 121 Weather Forecast
Offices (WFO). NWS field offices provide basic weather services such
as forecasts, severe weather warnings (e.g., tornadoes, flash
floods), warning preparedness, and, where applicable, aviation and
marine forecasts. Warning preparedness includes coordinating with
local emergency management, law enforcement agencies, and the media
on notification of and response to severe weather events. It also
relies on human observers to collect and report data on severe
weather events.
--------------------
\4 Weather Forecasting: Radar Availability Requirements Not Being
Met (GAO/AIMD-95-132, May 31, 1995) and Weather Forecasting: Unmet
Needs and Unknown Costs Warrant Reassessment of Observing System
Plans (GAO/AIMD-95-81, Apr. 21, 1995).
\5 See National Weather Service: Budget Events and Continuing Risks
Of Systems Modernization (GAO/T-AIMD-98-97, Mar. 4, 1998), Weather
Service Modernization: Risks Remain That Full Systems Potential Will
Not Be Achieved (GAO/T-AIMD-97-85, Apr. 24, 1997), Weather
Forecasting: Recommendations to Address New Weather Processing
System Development Risks (GAO/AIMD-96-74, May 13, 1996), Weather
Forecasting: NWS Has Not Demonstrated That New Processing System
Will Improve Mission Effectiveness (GAO/AIMD-96-29, Feb. 29, 1996),
Weather Forecasting: Improvements Needed in Laboratory Software
Development Processes (GAO/AIMD-95-24, Dec. 14, 1994), and Weather
Forecasting: Systems Architecture Needed for National Weather
Service Modernization (GAO/AIMD-94-28, Mar. 11, 1994).
\6 High-Risk Series: An Overview (GAO/HR-95-1, Feb. 1995) and
High-Risk Series: Information Management and Technology
(GAO/HR-97-9, Feb. 1997).
NEXRAD: A BRIEF OVERVIEW
---------------------------------------------------------- Letter :2.1
NEXRAD is a Doppler radar\7 system that measures wind velocity in
severe weather, tracks storm movement and intensity, and generates
data and imagery for forecasters and other users, such as air traffic
controllers. There are 141 operational NEXRADs in the conterminous
United States: 120 are operated by NWS and 21 are operated by the
Department of Defense.\8 The system allows forecasters at each
weather office to access radar information via dedicated and dial-up
connections to neighboring radars. This information is very
important for observing and tracking significant weather. The
reported cost of the NEXRAD program was nearly $1.5 billion. NWS
reports that the new radars have helped to increase the accuracy and
timeliness of warnings for severe thunderstorms, tornadoes, and other
hazardous weather events.
In 1995, we reported that NWS did not know if its radars were meeting
the availability requirement because it was not monitoring
availability effectively. We recommended that NWS analyze and
monitor NEXRAD system availability on a site-specific basis and
correct any shortfalls in system availability that this analysis
shows.\9 NWS concurred with these recommendations and began
monitoring system availability on a site-specific basis. However, as
we reported in our February 1997 high-risk report, not all NEXRADs
were meeting the availability requirement.\10
Each NEXRAD consists of three major subsystems--the radar data
acquisition (RDA) subsystem, the radar product generator (RPG)
subsystem, and the principal user processor (PUP) subsystem--and
associated communications among these subsystems. Each NEXRAD
includes about 400,000 lines of code for operating the radar,
processing radar signals, generating and transmitting data, and
displaying data products.
The RDA consists of a 10 centimeter wavelength Doppler weather radar
that collects the raw data to, among other things, (1) measure wind
velocity in severe weather, (2) provide improved estimates of
precipitation amounts, and (3) track storm movement and intensity.
The technology needed to perform this function includes an antenna,
pedestal, radome (a dome-shaped covering to protect the antenna),
transmitter, and receiver. Included in the RDA unit is hardware and
software necessary for a variety of control functions, including
signal processing, monitoring, and error detection, as well as
archiving the radar data. A computer processes the radar signals to
create digital data that can be further processed by the RPG.
The RPG includes all hardware and software necessary for turning the
data into displayable data products. Specifically, the RPG provides
real-time generation, storage, and distribution of products for
users. It includes hardware and software required for system
control; status monitoring; and error detection, archiving, and data
processing.
The PUP is a workstation that consists of the hardware and software
required for the request, display, local storage and annotation, and
distribution of products by forecasters. It also includes the
hardware and software required for local control, status monitoring,
archiving, and communicating with other users. The PUP maintains a
dedicated communication link to the RPG located on-site, and it
routinely receives NEXRAD products. The PUP also has the capability
to access data from RPGs at other NEXRAD sites. In addition, under
an NWS administered NEXRAD information dissemination service, NWS has
set aside four communications ports to allow access by commercial
companies that provide data to other government agencies and the
public. Figure 1 shows the key NEXRAD subsystems for a typical NWS
weather forecast office.
Figure 1: Key NEXRAD
Subsystems
(See figure in printed
edition.)
--------------------
\7 Doppler radar is used to determine the speed and direction of rain
or snow particles, cloud droplets, or dust moving toward or away from
the radar. The radar accomplishes this by sending out a pulse using
a stable frequency and then measuring the changing frequencies as the
distances between the radar and the object changes.
\8 FAA operates seven NEXRADs in Alaska, four in Hawaii, and one in
Puerto Rico.
\9 GAO/AIMD-95-132.
\10 GAO/HR-97-9.
SULPHUR MOUNTAIN NEXRAD
OVERVIEW
---------------------------------------------------------- Letter :2.2
The Sulphur Mountain NEXRAD was delivered for installation during
November 1993, tested from January 1994 through March 1994, accepted
in March 1994, and commissioned in December 1994. It is located in
southern Ventura County near the communities of Ojai and Sulphur
Springs, controlled by the Los Angeles/Oxnard weather forecast office
(WFO), and serves Los Angeles, Ventura, San Luis Obispo, and Santa
Barbara counties. Prior to installation of this weather radar, no
radar precipitation estimates were available for the Los Angeles
area.
The Los Angeles/Oxnard WFO also uses radar images from NEXRADs
located in Santa Ana, and Vandenberg and Edwards Air Force bases.
According to Los Angeles/Oxnard WFO officials, the four NEXRADs cover
the following counties or parts thereof:
Sulphur Mountain NEXRAD - eastern Santa Barbara County and offshore
waters, Ventura County and offshore waters, western Los Angeles
County and offshore waters.
Vandenberg Air Force Base NEXRAD - San Luis Obispo County and
offshore waters, Santa Barbara County and offshore waters.
Santa Ana NEXRAD - eastern Los Angeles County and offshore waters.
Edwards Air Force Base NEXRAD - extreme northern Ventura County,
northern Los Angeles County.
According to the National Weather Service, the offshore waters
covered by these four NEXRADs are essential to obtain advance warning
of storms as they approach the California coast. See figure 2 for
the counties served by the Los Angeles/Oxnard WFO and the locations
of the four NEXRADs used by this office.
Figure 2: Counties Served by
the Los Angeles/Oxnard Weather
Forecast Office and Locations
of NEXRADs Used by This Office
(See figure in printed
edition.)
SOUTHERN CALIFORNIA
TOPOGRAPHY AND CLIMATE
---------------------------------------------------------- Letter :2.3
Southern California has some of the steepest terrain in the United
States. The steep mountains and the Pacific Ocean create ideal
conditions for the orographic enhancement of rainfall.\11 This
terrain combined with the fact that the soil does not readily absorb
moisture make the rivers in this area prone to flooding during heavy
rains. NWS officials told us that the heaviest rains that produce
flooding in this area occur in the winter and typically approach from
the southwest.
--------------------
\11 As moist air moves up a mountain slope, it is cooled and the
moisture condenses forming clouds. If lifted far enough,
precipitation occurs. The effect of precipitation forming simply
from winds encountering mountainous terrain is called orographic
precipitation.
OVERVIEW OF THE ROSE
INSTITUTE STUDY
---------------------------------------------------------- Letter :2.4
When residents of the Upper Ojai Valley were informed that NWS was
installing a weather radar system on Sulphur Mountain, they became
concerned about the health effects of microwave radiation and asked
the Rose Institute of State and Local Government at Claremont McKenna
College to conduct a preliminary review of the issues.
In August 1997, the Rose Institute issued the report, The National
Weather Service's Tower in the Upper Ojai: A Case History. The
report's conclusions were:
-- "The initial siting decision seems to have been made without
full compliance with ordinary regulatory procedures; and the
administrator of the National Weather Service has issued
incorrect and misleading statements in defense of the selection
of the site."
-- "There is evidence that the Sulphur Mountain site prevents
NEXRAD from performing its mission of accurate, timely warning
of flash flooding in the San Gabriel mountain foothills, severe
weather in the Basin or wind shear data for the Basin airports."
-- "There is evidence that Sulphur Mountain radar fails to provide
the low-level data necessary to predict wind shear and clear air
turbulence for Los Angeles International Airport and the
Burbank/Pasadena Airport on a timely basis."
-- "Residents of the Sulphur Mountain area have been adversely
affected, property values have dropped significantly, and the
ability to sell property has virtually disappeared because of
the presence of the radar. The National Weather Service has
consistently refused to deal openly with the health issue raised
by siting the radar in a residential area."
In November 1997, the NWS responded to the Rose Institute report and
stated that it was "replete with misinformation concerning weather
radars, weakly supported opinions, and several paradoxical
conclusions."
Subsequent to that response, the Rose Institute issued another report
in May 1998 that expanded on some of the issues raised in its
November report, while also raising additional concerns, including
whether the Sulphur Mountain NEXRAD coverage is needed since "ninety
percent of the area that the Sulphur Mountain tower was installed to
cover is covered by other NEXRAD stations."
OBJECTIVES, SCOPE, AND
METHODOLOGY
------------------------------------------------------------ Letter :3
The objectives of our review were to determine whether the Sulphur
Mountain NEXRAD (1) can provide timely and accurate information for
warning of flash floods and (2) is intended to provide low-level data
necessary to predict wind shear for Los Angeles International
Airport.
To determine whether the Sulphur Mountain NEXRAD can provide timely
and accurate information for warning of flash floods, we
-- reviewed documentation on NEXRAD and interviewed NWS officials
to determine what information NEXRAD provides that is used to
issue flash flood warnings,
-- interviewed NWS officials at the Los Angeles/Oxnard WFO to
determine what other systems, in addition to NEXRAD, are used to
issue flash flood warnings,
-- reviewed flash flood events (this information was obtained from
the Storm Data database located in Silver Spring, Maryland) and
flash flood warnings (this information was obtained from the
National Climatic Data Center located in Asheville, North
Carolina) that occurred in Ventura and Los Angeles counties\12
from January 1992 through February 1998 to determine the
accuracy and timeliness of flash flood warning lead times prior
to and after the installation of the Sulphur Mountain NEXRAD
[Note: In calculating the warning lead times, we used the
initial flash flood warning in our analysis and excluded all
flash flood warning extensions that were issued after the
initial warning.]
-- supplemented the flash flood event and warning data obtained
from the Storm Data database and the National Climatic Data
Center, respectively, with local flash flood event and warning
information from the Los Angeles/Oxnard WFO since the national
databases were incomplete,
-- verified our analysis of the flash flood event and warning data
with NWS Los Angeles/Oxnard WFO officials,
-- compared the timeliness of the flash flood warning lead times to
the requirement specified in Commerce's 1999 Annual Performance
Plan,
-- obtained and reviewed Sulphur Mountain NEXRAD availability data
from the Engineering Management Reporting System for the period
from October 1995 through March 1998 to determine if the Sulphur
Mountain radar was meeting the 96 percent availability
requirement,
-- reviewed three flash flood events that occurred on February 3,
6, and 23, 1998, to determine how data from the Sulphur Mountain
NEXRAD is used in combination with rain gage information to
issue flash flood warnings, and
-- interviewed the following users to obtain their views of the
quality, timeliness, and utility of the Sulphur Mountain NEXRAD
data: officials from the Flood Control Department of the
Ventura County Public Works Agency; the Los Angeles County
Department of Public Works; Point Mugu Naval Air Warfare Center;
U.S. Army Corps of Engineers, Los Angeles District, Reservoir
Regulation Section; Ventura County Sheriff's Department; the
Assistant City Administrator from the Emergency Preparedness
Division, City of Los Angeles; weathercasters from KCBS-TV and
KCAL-TV; and the director of Fox Weather, a private
meteorological service.
To determine whether the Sulphur Mountain NEXRAD is intended to
provide low-level data necessary to predict wind shear for Los
Angeles International Airport, we
-- reviewed documentation that established NEXRAD's requirements,
-- reviewed FAA documentation describing systems that predict wind
shear at airports, including those systems at Los Angeles
International Airport, and
-- interviewed NWS and FAA officials.
We performed our work at the National Oceanic and Atmospheric
Administration (NOAA) and NWS headquarters in Silver Spring,
Maryland, and at the Los Angeles/Oxnard WFO in Oxnard, California.
Our work was performed from February 1998 to September 1998, in
accordance with generally accepted government auditing standards.
The Secretary of Commerce provided written comments on a draft of
this report. These comments are discussed in the "Agency Comments"
section of this report and are reprinted in appendix II. In
addition, FAA officials, including the Acting Product Lead for Wind
Shear and Radar, provided oral comments on a draft of this report.
FAA's comments are also discussed in the "Agency Comments" section.
--------------------
\12 Ventura and Los Angeles counties were selected because they are
two counties that the Los Angeles/Oxnard WFO had responsibility for
from January 1992 through February 1998 (from January 1992 to October
1993 the office was located in Los Angeles), and because they are the
two primary counties that the Sulphur Mountain NEXRAD covers.
SULPHUR MOUNTAIN NEXRAD HAS
CONTRIBUTED TO MORE ACCURATE
AND TIMELY FLASH FLOOD
WARNINGS, BUT IS NOT ALWAYS
AVAILABLE
------------------------------------------------------------ Letter :4
The accuracy and timeliness of flash flood warnings has increased in
Los Angeles and Ventura counties since the Sulphur Mountain NEXRAD
became operational in December 1994. Although other systems can
contribute to the improved timing of the flash flood warnings, NWS
officials believe that the system that is primarily responsible for
improved flash flood warning lead times in Ventura and Los Angeles
counties is the Sulphur Mountain NEXRAD. Users, in addition to NWS,
also told us that they rely heavily on the Sulphur Mountain NEXRAD to
alert the public to flash floods. Despite the improvements in flash
flood warnings and overall user satisfaction, the Sulphur Mountain
NEXRAD is not always available the required amount of time.
ACCURACY AND TIMELINESS OF
FLASH FLOOD WARNINGS HAS
IMPROVED SINCE SULPHUR
MOUNTAIN NEXRAD BECAME
OPERATIONAL
---------------------------------------------------------- Letter :4.1
The Department of Commerce's Fiscal Year 1999 Annual Performance Plan
specifies as one objective to "continue improving the timeliness and
accuracy of short-term environmental predictions that have immediate
impact on individuals and many sectors of the economy." It further
states that for fiscal year 1999, the goal is to increase flash flood
warning lead time to 42 minutes.
The accuracy and timeliness of flash flood warnings has increased in
Los Angeles and Ventura counties since the Sulphur Mountain NEXRAD
was commissioned in December 1994. From January 1992 through
December 1994, 18 flash flood events were reported in Ventura and Los
Angeles counties. There was no advanced warning for any of the 18
events. However, from January 1995 through February 1998, advanced
warnings were issued for 17 of the 22 reported events; and the
average warning lead time for these was just over 2 hours. For the
17 events, the warning lead time ranged from 8 minutes to 3 hours and
50 minutes, and exceeded the fiscal year 1999 flash flood warning
lead time goal of 42 minutes for 14 of the 17 events. Figure 3
displays flash flood warning lead times for the 40 flash flood events
that occurred in Ventura and Los Angeles counties from January 1992
through February 1998.
Figure 3: Warning Lead Time
for Flash Flood Events for
Ventura and Los Angeles
Counties (January 1992 through
February 1998)
(See figure in printed
edition.)
Source: Los Angeles/Oxnard WFO, Oxnard, CA; National Climatic Data
Center, Asheville, NC; NWS Headquarters, Silver Spring, MD.
Concerning the five events since January 1995 that were not preceded
by a warning, Los Angeles/Oxnard WFO officials stated that two of the
events were incorrectly recorded as flash floods and two were flash
flood warning extensions that were issued after the initial warning
and, therefore, none of the four should be counted as missed events.
According to the Los Angeles/Oxnard WFO meteorologist-in-charge, one
of the incorrectly recorded events was an urban flood event,\13 while
the other was the result of a controlled water release into the Los
Angeles River. However, because no documentation was provided to
substantiate NWS' statements, we classified all five as missed
events.
Another measure of accuracy is the number of false warnings that
occurred. From January 1992 through December 1994, NWS data shows
that there were three false flash flood warnings, while from January
1995 through February 1998, NWS data shows five false flash flood
warnings. See appendix I for details on each of the 40 events listed
in figure 3 (e.g., date of the event, time of the flash flood, time
the warning was issued), as well as the dates of the false warnings.
Although NEXRAD is not the only source of data on which storms are
tracked, Los Angeles/Oxnard WFO officials told us that the Sulphur
Mountain NEXRAD is the primary reason for the increase in advanced
warning lead time because it provides advanced warning of heavy
precipitation oftentimes before severe weather hits the California
coast. NWS officials told us that well before the NEXRAD imagery is
used to issue a flash flood warning, forecasters use other sources of
information to track storms as they approach the west coast,
primarily high resolution satellite imagery from the GOES-Next
satellites and detailed numerical models. However, as storms
approach the counties covered by the Los Angeles/Oxnard WFO, the
detailed imagery from the Sulphur Mountain NEXRAD is used to issue
flash flood warnings, along with the neighboring NEXRADs (i.e.,
Vandenberg Air Force Base, Edwards Air Force Base, and Santa Ana).
NEXRAD estimates of precipitation rate and amount are extremely
important for flash flood forecasting; however, NWS officials at the
Los Angeles/Oxnard WFO told us that these estimates are not always
exact and are supplemented with rainfall sensors and human observers.
For example, radar reflectivity is affected by many factors,
including precipitation growth, evaporation, and type; thus, the
precipitation observed by the NEXRAD beam is not absolute and may not
be exactly representative of that reaching the ground. Therefore, to
improve NEXRAD precipitations estimates, Los Angeles/Oxnard WFO
officials rely on "ground truth" that is provided by surface
observation networks\14 and human observations.
--------------------
\13 NWS' Operations Manual defines an urban flood event as flooding
to streets and low-lying areas, such as railroad underpasses and
urban storm drains. The manual states that urban flooding is mainly
only an inconvenience and is generally not life threatening nor is it
significantly damaging to property.
\14 These surface observation networks are referred to as the
Automated Local Evaluation in Real Time (ALERT) network. The ALERT
network uses remote sensors (i.e., rain gages) from various sources,
including, privately owned companies, county flood control agencies,
and the Automated Surface Observing System (ASOS) which transmit data
to a central computer in real time.
USERS SAY SULPHUR MOUNTAIN
NEXRAD PROVIDES VALUABLE,
ACCURATE, AND TIMELY DATA
---------------------------------------------------------- Letter :4.2
NWS officials and other users of the Sulphur Mountain NEXRAD data
told us that the information it provides is valuable, accurate, and
timely. NWS officials provided us with detailed case studies of
three February 1998 El Nino-related flash flood events that show how
the Sulphur Mountain NEXRAD imagery was used to issue flash flood
warnings.\15 For example, on February 6, 1998, NWS issued a flash
flood warning for southern Ventura and western Los Angeles counties
at 8:35 a.m. based on the Sulphur Mountain NEXRAD information. At
8:40 a.m., the Sulphur Mountain NEXRAD showed heavy thunderstorms
moving on shore near Ventura Harbor. By 10 a.m., rafts were needed
to evacuate a mobile home park in Camarillo. As the storm moved
eastward, a 20-foot sinkhole opened near Moorpark road in Thousand
Oaks and mudslides closed the Pacific Coast highway in Malibu.
Eight of the nine other users of Sulphur Mountain NEXRAD data we
interviewed told us that they are pleased with the information it
provides, and that it was an important tool for performing their jobs
accurately and timely. For example, officials from the Los Angeles
County Department of Public Works, who are responsible for
constructing, operating, and maintaining the flood control and water
conservation facilities in Los Angeles County, told us that the
Sulphur Mountain NEXRAD has significantly improved the quality and
quantity of radar information they receive and that it is
substantially more detailed, accurate, and timely than previous
radars. An official from the Point Mugu Naval Air Warfare Center,
who provides day-to-day forecasts during flight briefings to ensure
the safety of aircraft, described the Sulphur Mountain NEXRAD data as
"critical." The Director of Emergency Services for Ventura County
considers the radar "to be an effective tool for identifying the
appropriate level of response for county emergency services during
inclement weather." The Los Angeles District Corps of Engineers,
which manages water control projects in Southern California,
including 10 Corps of Engineers reservoirs in the Los Angeles area
that provide flood protection to downstream areas, said that data
from the radar "has proven to be a very valuable water management
tool." One user, the director of Fox Weather, a private
meteorological service, said that the radar was less useful for
Ventura County than for the Los Angeles area because it had not
significantly improved his ability to provide precipitation estimates
for his clients. NWS officials acknowledge that precipitation
estimates are not always exact and therefore are supplemented with
surface observation networks and human observers.
Several of the users also described specific incidents where data
from the Sulphur Mountain NEXRAD was especially useful in informing
the public and protecting lives and property. For example, the TV
weathercaster for KCBS-TV used the radar during an intense storm on
December 6, 1997, to track the storm and give people in Ventura
County up-to-the-minute reports. With the data from the Sulphur
Mountain NEXRAD, he was able to provide warnings to specific
locations before the storm occurred. In addition, the program
administrator of the Ventura County Sheriff's Department's Office of
Emergency Services told us that 48 hours after the La Conchita
landslide in March 1995, data from the Sulphur Mountain radar was
used to provide a warning of another severe storm moving into the La
Conchita area. The warnings, which were not available from other
NEXRADs in the area, provided ample time to evacuate already deployed
emergency services personnel, ground helicopters, and take other
safety precautions.
--------------------
\15 These three events occurred on February 3, 6, and 23, 1998.
SULPHUR MOUNTAIN NEXRAD IS
NOT MEETING AVAILABILITY
REQUIREMENT
---------------------------------------------------------- Letter :4.3
System availability is defined as the time that a system is operating
satisfactorily, expressed as a percentage of the time the system is
required to be operational.\16
NWS requires that each NEXRAD be available 96 percent of the time.
We reported in May 1995 that according to NWS officials, the 96
percent requirement is based on an analysis that considered factors
such as equipment reliability, staff costs, and spare part costs.\17
These officials stated that the additional costs (for example,
redundant systems, spare parts, and additional maintenance
technicians) associated with achieving availability above 96 percent
were not worth the added benefits.
The Sulphur Mountain NEXRAD is not consistently meeting the 96
percent availability requirement. From October 1995 through March
1998, NWS' engineering management reporting system (EMRS) reports
show that the Sulphur Mountain NEXRAD did not meet the 96 percent
requirement for 10 of the 30 months reviewed. (See figure 4.)
Figure 4: Sulphur Mountain
NEXRAD Availability Fiscal
Years 1996, 1997, 1998 (Through
March 1998)
(See figure in printed
edition.)
(See figure in printed
edition.)
(See figure in printed
edition.)
Source: NWS. We did not independently verify these data.
NWS officials from the Los Angeles/Oxnard weather forecasting office
told us that the Sulphur Mountain NEXRAD is not consistently meeting
the 96 percent availability requirement because of component failures
and the time-consuming logistics process associated with fixing the
failed components. If the NEXRAD is down for more than 28 hours in a
30-day month, the 96 percent availability requirement will not be
met. The Los Angeles/Oxnard WFO technicians who troubleshoot outages
and are responsible for making repairs told us that most of the
outages associated with the months when the availability requirement
was not met required ordering a part that was not on hand. They
added that it usually takes at least 24 hours for the parts to arrive
after they are ordered. The technicians told us that they strive to
meet the 96 percent requirement, but that it is very difficult,
considering that it takes 1 hour to get to the site from the Los
Angeles/Oxnard WFO, time to analyze the problem, usually 24 hours to
receive the needed part, 1 hour to get back to the site, and time to
repair the NEXRAD.
The technicians told us that they have tried using other shipping
companies to hasten delivery of replacement parts, but these efforts
have not resulted in improved delivery times. The technicians also
told us that deliveries of parts are sometimes delayed because some
ordered parts are not in stock and some replacement parts have been
defective. For example, in May 1996, when the NEXRAD's availability
was only 90.3 percent, there was a 48-hour logistics delay because
the required part was out of stock. In addition, the low
availability reported in February 1997 occurred because the ordered
part was defective.
Until the Sulphur Mountain NEXRAD consistently meets the 96 percent
availability requirements, NWS risks not having the data it needs to
accurately and quickly predict flash floods and other severe weather.
NWS headquarters officials acknowledged the availability shortfalls
and stated that they are monitoring the failure rates of parts and
are attempting to reduce the failure rates or to more quickly replace
the parts that fail most often. For instance, they told us that they
are installing fans to keep the transmitter, a component that has
been unreliable since the inception of the NEXRAD program, from
overheating. They added that the NEXRAD program has a 6-year
modification plan which, among other things, identifies deficiencies
in hardware performance and reliability and prioritizes NWS'
improvement activities. They are also attempting to stock those
spare parts that fail frequently at each location; however, they
added that their budget does not allow for a full set of spares at
each location. In addition, NWS officials told us that spare part
inventories at the National Logistics Supply Center have recently
been bolstered to replenish those stocks that were below desired
levels. Finally, NWS officials told us that they are working with
different shipping companies to improve the shipping process.
--------------------
\16 NWS refers to this percentage as service availability.
\17 Weather Forecasting: Radar Availability Requirements Not Being
Met (GAO/AIMD-95-132, May 31, 1995).
NEXRAD IS NOT INTENDED TO
PROVIDE DATA THAT ARE USED TO
PREDICT WIND SHEAR AT AIRPORTS
------------------------------------------------------------ Letter :5
Although NEXRAD uses doppler technology that is capable of detecting
changes in wind direction, such as wind shear and atmospheric
conditions associated with tornadoes and other severe storms, the
detection of low-level wind shear at airports is not part of the
mission of the NEXRAD network, and it is not specifically designed to
do that. FAA uses three different systems, either singly or in
tandem, to predict wind shear at airports -- Terminal Doppler Weather
Radar (TDWR), Weather Systems Processor (WSP), and Low Level Wind
Shear Alert System (LLWAS). Los Angeles International currently has
LLWAS and is scheduled to get WSP in 2001.
NEXRAD WAS NOT DESIGNED TO
DETECT WIND SHEAR AT
AIRPORTS
---------------------------------------------------------- Letter :5.1
NEXRAD was originally designed to be a weather surveillance radar for
general weather observation. It was not designed to detect
wind-shear at airports. According to FAA officials, in the early
1980s, FAA studied whether NEXRAD could meet its requirements for
detecting wind shear and microbursts.\18 The study concluded that
NEXRAD could not produce timely warnings of wind shear or other low
altitude phenomena at the required 1 minute update rate required by
FAA.\19 NEXRAD information is updated every 5 to 6 minutes.
In addition to not being designed to detect wind shear at airports,
NEXRADs are not located to serve airports. NEXRADs were located
throughout the contiguous United States to optimize national coverage
for general weather observation. On the basis of NWS', Department of
Defense's, and FAA's collective mission needs and the Weather Service
Modernization Act, which mandates that the Secretary of Commerce
certify that there will be no degradation in radar coverage at the
10,000-foot level prior to closing, consolidating, automating, or
relocating any of NWS' field offices, the three agencies negotiated
the radars' locations to meet tri-agency radar coverage
requirements.\20
--------------------
\18 Wind shear is defined as a sudden change in wind direction that
occurs at low altitudes, and a microburst is a form of wind shear.
\19 Because microbursts develop quickly and move rapidly, FAA
requires 1 minute updates of radar information.
\20 The 10,000-foot level is significant because this is the
elevation at which the coverage range of an individual NEXRAD is
measured. The ascending radar beam loses its reliability about 125
miles from the radar. At this distance, the lowest part of the beam
is approximately 10,000 feet off the ground. Therefore, each radar
has a coverage diameter of 250 miles. The 250 mile cylinders were
the basis for siting NEXRADs to ensure adequate national coverage.
FAA USES THREE SYSTEMS TO
DETECT WIND SHEAR AT
AIRPORTS
---------------------------------------------------------- Letter :5.2
FAA uses three systems that are specifically designed to detect wind
shear at airports. TDWR is the "state of the art" wind shear
detection system that is currently being deployed at high traffic
airports that experience severe weather. TDWR is a Doppler radar,
typically located 8 to 12 miles from the airport, that is designed to
detect wind shear, microbursts, precipitation, and storm motion. Its
information update rates match the near real time requirement needed
during aviation landings and departures.
WSP is a modification to FAA's air traffic control airport
surveillance radar (ASR-9) that is to provide FAA with 80 to 95
percent of the capability of TDWR. WSP is to be installed at high to
moderate traffic airports that experience limited severe weather. It
adds a doppler processor to the ASR-9, giving it the capability to
detect microbursts, gust fronts, precipitation intensity, storm cells
and the motion of shifting gust fronts. A prototype WSP is installed
in Albuquerque, New Mexico, and a production contract was awarded on
September 14, 1998.
LLWAS is a network of anemometers that were originally installed in
the 1970s. LLWAS is used to supplement TDWR at nine high-traffic
airports at greatest risk of severe weather and it is used at other
airports that will not get TDWR or WSP--typically lower traffic
airports. Los Angeles International currently has LLWAS and since it
is an airport designated as having high to moderate traffic that
typically experiences limited severe weather, it is scheduled to get
WSP in 2001.
CONCLUSIONS
------------------------------------------------------------ Letter :6
The accuracy and timeliness of flash flood warning lead times has
improved since the Sulphur Mountain NEXRAD was commissioned in
December 1994. Although other systems, including the sophisticated
network of ground sensors, have contributed to this improvement, NWS
officials told us that the Sulphur Mountain NEXRAD is the primary
reason for the improvement. NWS feedback on the NEXRAD's performance
is consistent with that of other users, who find its data accurate,
timely, and valuable.
However, the Sulphur Mountain NEXRAD is not consistently meeting its
availability requirement, thus increasing the risk that NWS and other
users will not always have the data needed to accurately and quickly
predict flash floods and other severe weather. The risk is more
serious in the winter months when Southern California experiences
flash flooding. Until the Sulphur Mountain NEXRAD consistently meets
the required availability requirement, lives and property are at
increased risk. Consistent with our 1995 recommendation to correct
shortfalls in NEXRAD system availability,\21 NWS headquarters
officials told us they are taking steps to improve systems
availability. However, as the Sulphur Mountain NEXRAD data show,
these steps have not been sufficient.
It was never the intent of the NEXRAD systems to provide detailed
data used to predict wind shear at airports, and NEXRAD was not
designed for this purpose. FAA uses other systems to perform this
mission.
--------------------
\21 GAO/AIMD-95-132.
RECOMMENDATION
------------------------------------------------------------ Letter :7
Since the Sulphur Mountain NEXRAD is not always available as
required, we recommend that the Secretary of Commerce direct the NOAA
Assistant Administrator for Weather Services to determine all the
reasons why the Sulphur Mountain NEXRAD is not meeting the 96 percent
availability requirement and to correct the problems so that the
radar is available as required.
AGENCY COMMENTS
------------------------------------------------------------ Letter :8
In commenting on a draft of this report, the National Weather Service
concurred with our recommendation and mentioned several key
activities that are planned to improve radar availability. This
written response is reprinted in appendix II. In addition, FAA
officials said that the information presented in this report is
accurate.
---------------------------------------------------------- Letter :8.1
We are providing copies of this report to the Secretaries of Commerce
and Transportation, the Director of the Office of Management and
Budget, and interested congressional committees. Copies will be
available to others upon request. If you have any questions about
this report, please call me at (202) 512-6253, or Dave Powner,
Assistant Director, at (202) 512-4348. We can also be reached by
e-mail at [email protected] and [email protected],
respectively. Major contributors to this report are listed in
appendix III.
Joel C. Willemssen
Director, Civil Agencies Information Systems
FLASH FLOOD EVENTS AND WARNINGS
FOR VENTURA AND LOS ANGELES
COUNTIES FROM JANUARY 1992 THROUGH
FEBRUARY 1998\1
=========================================================== Appendix I
Time flash Counties
flood affected by Warning lead
event Time warning event and/or time
Date occurred\a issued warning (hours:minutes)
-------------- -------------- -------------- -------------- ----------------
(1) 2/10/92 1230 hours 1345 hours Ventura /Los -1:15
Angeles
(2) 2/10/92 1600 hours 2012 hours Los Angeles -4:12
(3) 2/11/92 0959 hours 0959 hours Los Angeles 0:00
(4) 2/12/92 0937 hours 0937 hours Ventura /Los 0:00
Angeles
(5) 2/12/92 1302 hours 1302 hours Los Angeles 0:00
(6) 2/15/92 0545 hours Ventura/Los No warning
Angeles
(7) 8/13/92 0915 hours Los Angeles No warning
(8) 1/13/93 All day Ventura/Los No warning
Angeles
(9) 1/13/93 2110 hours Ventura No warning
(10) 1/18/93 0940 hours 0940 hours Ventura/Los 0:00
Angeles
(11) 2/8/93 All day 1115 hours Ventura/Los 0:00
Angeles
(12) 2/18/93 All day 1721 hours Ventura/Los 0:00
Angeles
(13) 2/7/94 1500 hours 1710 hours Los Angeles -2:10
(14) 2/7/94 2100 hours 2230 hours Los Angeles -1:30
(15) 2/17/94 0740 hours Los Angeles No warning
(16) 2/20/94 0345 hours Los Angeles No warning
(17) 3/7/94 1645 hours Los Angeles No warning
(18) 3/24/94 1630 hours Los Angeles No warning
(19) 1/4/95 0930 hours Ventura No warning
(20) 1/4/95 1000 hours 0850 hours Los Angeles 1:10
(21) 1/7/95 1700 hours 1735 hours Los Angeles -0:35
(22) 1/9/95 0300 hours 2330 hours Ventura 3:30
(23) 1/10/95 0600 hours 0300 hours Los Angeles 3:00
(24) 1/10/95 0717 hours 0415 hours Ventura 3:02
(25) 1/10/95 0834 hours 0600 hours Los Angeles 2:34
(26) 3/10/95 2150 hours 1850 hours Ventura 3:00
(27) 3/10/95 2330 hours 1940 hours Los Angeles 3:50
(28) 1/20/97 1352 hours Los Angeles No warning
(29) 2/3/98 0600 hours 0448 hours Ventura 1:12
(30) 2/6/98 0930 hours 0835 hours Ventura/Los 0:55
Angeles
(31) 2/6/98 0930 hours 0910 hours Ventura 0:20
(32) 2/6/98 1135 hours 0955 hours Los Angeles 1:40
(33) 2/6/98 1038 hours 1030 hours Ventura/Los 0:08
Angeles
(34) 2/7/98 2040 hours 1705 hours Ventura 3:35
(35) 2/7/98 2205 hours 1950 hours Los Angeles 2:15
(36) 2/23/98 1115 hours 0935 hours Ventura 1:40
(37) 2/23/98 1500 hours 1240 hours Ventura/Los 2:20
Angeles
(38) 2/23/98 1630 hours 1600 hours Los Angeles 0:30
(39) 2/23/98 2255 hours 2255 hours Los Angeles 0:00
(40) 2/24/98 0300 hours 0300 hours Los Angeles 0:00
--------------------------------------------------------------------------------
\a The event and warning times are recorded using a 24-hour clock,
e.g., 1400 hours is 2 p.m.
(See figure in printed edition.)Appendix II
--------------------
\1 No flash flood events or warnings were recorded during 1996.
Three false flash flood warnings were recorded prior to the
commissioning of the Sulphur Mountain NEXRAD: 2/12/92, 2/15/92, and
2/8/94. Five false flash flood warnings were recorded after the
commissioning of the Sulphur Mountain NEXRAD: 9/2/97, three on
12/6/97, and 2/3/98.
COMMENTS FROM THE DEPARTMENT OF
COMMERCE
=========================================================== Appendix I
(See figure in printed edition.)
MAJOR CONTRIBUTORS TO THIS REPORT
========================================================= Appendix III
ACCOUNTING AND INFORMATION
MANAGEMENT DIVISION, WASHINGTON,
D.C.
Keith A. Rhodes, Technical Director
David A. Powner, Assistant Director
Barbarol J. James, Evaluator-in-Charge
Robert D. Faggart, Information Systems Analyst
*** End of document. ***